The answer is definitely C.) their molecules move at the same average speed
Answer:
(C) apparently written incorrectly - it should be 29.9 +- .3 K
(read 29.9 plus or minus .3 K)
Answer: An 8 kg book at a height of 3 m has the most gravitational potential energy.
Explanation:
Gravitational potential energy is the product of mass of object, height of object and gravitational field.
So, formula to calculate gravitational potential energy is as follows.
U = mgh
where,
m = mass of object
g = gravitational field = 
h = height of object
(A) m = 5 kg and h = 2m
Therefore, its gravitational potential energy is calculated as follows.

(B) m = 8 kg and h = 2 m
Therefore, its gravitational potential energy is calculated as follows.

(C) m = 8 kg and h = 3 m
Therefore, its gravitational potential energy is calculated as follows.

(D) m = 5 kg and h = 3 m
Therefore, its gravitational potential energy is calculated as follows.

Thus, we can conclude that an 8 kg book at a height of 3 m has the most gravitational potential energy.
Explanation:
Average acceleration is change in velocity over time.
a = Δv / Δt
a = (22.0 m/s − (-25.0 m/s)) / 0.00350 s
a = 13,400 m/s²